Method for tin plating bunched and braided wire



ventional strip or wire plating equipment.

United States Patent METHOD FOR TIN PLATING BUNCHED AND BRAIDED WIRE Frederick A. Lowenheim, Plainfield, and Herbert E. Hirschland, Cranford, N. J., assignors to Metal & Thermit Corporation, New York, N. Y., a corporation of New Jersey No Drawing. Application October 21, 1950, Serial No. 191,484

6 Claims. (Cl. 20427) This invention relates to the manufacture of tin plated wire composed of a plurality of constituent strands which are woven or twisted together to form what is known as bunched wire or cable, or woven to form a braid. More particularly, the invention relates to a process for electroplating tin simultaneously on all the strands of a formed cable or braid without joining or fusing one strand to another, thus producing a flexible tin plated wire cable or wire braid.

Such cabled or braided wire is useful as, among other things, an electrical conductor, the tin coating thereon being of assistance in subsequent soldering operations where it is desired to solder the'cable or braid. Also, in the case of copper containing wire the tin coating prevents contact between the wire and rubber-containing insulating materials and thus avoids the deterioration of the rubber by the copper. It is, of course, necessary in this connection that the tinned cable or braid shall be flexible.

Heretofore tinned braid or cable has been fabricated by tinning individual strands, as by hot dipping, and then weaving or twisting the tinned strands to form the final product. Since the individual strands are usually of very fine gauge, they have a relatively low strength, and because of this factor there has been an appreciable incidence of breakage in the tinning vessel. On the other hand, if braid or cable as such is attempted to be tinned by hot dipping, the constituent strands of the final product would be completely joined together and the product would lose all of its flexibility as well as take up excessive amounts of tin.

It has now been found that it is possible to fabricate tinned wire braid or cable by first twisting or weaving it from untinned individual strands, and then tin plating the braid or cable so formed in an electroplating bath to produce a product that is quite satisfactory. This surprising result is not all, for not only may a formed braid or cable be successfully tin plated as described, but the invention also enables flexible tinned braid or cable to be made at a production rate higher than in other known methods.

The weaving or twisting of the individual strands may be done by conventional methods and need not be described. The plating step may be carried out in con- An alkaline stannate plating solution is used, preferably comprising potassium stannate and potassium hydroxide, the stannate concentration ranging from about 0.25 to about 3.0 mols per liter, and the free potassium hydroxide ranging from about 0.15 to about 3.5 mols per liter. During the plating operation, the cathode current density should be about 30 to about 1000 amperes/ sq. ft., and the temperature of the bath should preferably lie between about 50 C. to substantially the boiling point of the bath. A sodium stannate bath may also be employed, the sodium stannate ranging from about 0.25 to about 0.5 mol per liter, the free sodium hydroxide from about 0.2 to about 0.6 mol per liter, the cathode current density from about 10 to about 100 amperes/ sq. ft., and the temperature from about 50 to about 80 C. The higher current densities are 2,737,483 Patented Mar. 6, 1956 compatible with high wire speeds through the plating bath, while lower current densities are suitable for low wire speeds. After the plating step, the tinned wire is rinsed and dried. While not necessary for a useful product, it is often desirable, and preferable, to subject the tinned wire to refiowing in a non-oxidizing atmosphere to improve the coating, as by brightening it. Any suitable refiowing method may be used, including induction heating and the use of hot oil. In the latter method, which is convenient, a suitable oil temperature is about 240 C. with a contact time of about 2 or 3 seconds, followed by a vapor degreasing step to remove the oil. At higher temperatures the contact time may be lower, and vice versa, but in every case the temperature must be above the melting point of tin.

In the plating operation, it is necessary to limit the amount of tin deposited on the wire in order to secure effective results. Plating should proceed until the amount of tin deposited is in the range of about 1 to about 2% by weight of the wire being plated. In some cases, the amount of tin deposited may be as high as 3% by weight of the wire, and in other cases as low as 0.5% by weight, but for most purposes about 1 to 2% by weight is preferred. Amounts of plated tin outside of these quantities will not result in a satisfactory product, for it will be either incompletely coated or else the constituent strands of the cable or braid will be joined together.

The following examples may illustrate the invention.

Example 1 An 8 ft. length of round 7/28 bunched copper wire or cable was placed in a potassium stannate bath containing 0.4 mol/liter of potassium stannate and 0.2 mol/liter of free potassium hydroxide. By 7/28 is meant that the wire was composed of 7 strands of 28 gauge wire. Plating of the wire was carried out for2 minutes, using a cathode current of 10 amperes and a bath temperature of 90 C. After the plating, the bunched wire was reflowed in hot fat for about 3 seconds at a temperature of 240 C. Examination of the wire showed a satisfactory flexible tinned product. The amount of tin deposited on the wire was 2.7% by weight of the wire.

The above experiment was repeated several times, except that different sizes of wire, i. e. lengths of l0/30, 26/30, and 16/30 bunched wire, were used. A satisfactory product in each case was obtained, the amount of Example 2 A sample of flat braided copper wire /2" wide x 19, thick x 3" long was plated in the bath of Example 1 for 5 minutes at /2 ampere current. It was then refiowed in hot fat as described. Examination showed it to be a good flexible tinned braid. The amount of tin deposited was 1.2% by weight of the braid.

Example 2 was repeated with other similar samples of braid except that the plating current and plating time were varied. In one case a current of 1 ampere for 1 minute was employed, in another /2 ampere for 3 minutes, and then 2 amperes for 2 minutes. In each case a good product was made, the amount of tin deposited in these cases being 0.48, 0.72, and 1.9% by weight, respectively.

A bunch of wire is commonly defined as the product of a stranding operation in which several wires are twisted together in the same direction and in a uniform manner into a rope-like form. A braid is defined as the product of crossing a number of strands diagonally in such a way that each strand passes alternately over and under one or more of the others. Braided wire is made on a machine that builds up a tube of interwoven wires of any number desired on the outside of a core or on a spindle. In the latter case the braided tube comes off the spindle and is usually rolled fiat to form a fiat flexible strip.

In general, metal articles consisting of adjacently lying, intertwisted metallic component strands, including mesh and link material may be satisfactorily tin plated with- 'out joining the individual strands to one another. The invention makes it possible to uniformly plate all of the individual strands, even those deeply buried in the article, without causing the article to lose its flexibility. The article itself may he composed of any metal which is capable of being tin plated.

In the light of the foregoing description, the following is claimed:

1. Process for making tin plated bunched or braided copper wire consisting of a plurality of fine gauge constituent strands regularly intertwisted or interwoven together, which comprises immersing untinned bunched or braided wire in a potassium stannate electroplating bath, said bath containing about 0.25 to about 3.0 mols per liter of potassium stannate and about 0.15 to about 3.5 mols per liter of free potassium hydroxide, operating said bath at a cathode current density of about 30 to about 1000 amperes per sq. ft. and a temperature of about 50 C. to substantially the boiling point of the bath, electroplating tin upon each of said strands of said wire to entirely cover each strand and until an amount of tin equal to about 1 to about 2% by weight of the wire has been plated, thereby forming a tinned bunched or braided wire in flexible condition each of whose constituent strands are plated with tin andseparated from adjacently lying strands, removing the wire from the bath and rinsing and drying the same, and heating the plated wire under non-oxidizing conditions to refiow the tin plate.

" 2. Process for making tin plated bunched or braided copper wire consisting of a plurality of fine gauge constituent strands regularly intertwisted or interwoven together, which comprises immersing untinned bunched or braided wire in a sodium stannate electroplating bath, said bath containing about 0.25 to about 0.5 mol per liter of sodium stannate and about 0.2 to about 0.6 mol per liter of free sodium hydroxide, operating said bath at a cathode current density of about to about100 amperes per sq. ft., and at a temperature of about 50 C. to about 80 C., electroplating tin upon each of said strands of said wire to entirely cover each strand and until an amount of tin equal to about 1 to about 2% by weight of the wire has been plated, thereby forming a tinned bunched or braided wire in flexible condition each of whose constituent strands are plated with tin and separated from adjacently lying strands, removing the wire from the bath and rinsing and drying the same, and heating the plated wire under non-oxidizing conditions to reflow the tin plate.

3. Process for making tin plated bunched or braided metal wire consisting of a plurality of fine gauge constituent strandsregularly intertwisted and interwoven together, said metal being capable of being tin plated and having a specific gravity of about 8.5, which comprises immersing untinned bunched or braided wire in an alkaline stannate electroplating bath, electroplating tin upon each of said strands of said wire to entirely cover each strand and until an amount of tin equal to about 1 to about 2% by weight of the wire has been plated, thereby forming a tinned bunched or braided wire in flexible'condition each of whose constituent strands are plated with tin and separated from adjacently lying strands, removing the wire from the bath and rinsing and drying the same, and heating the plated wire under non-oxidizing conditions to refiow the tin plate.

4. Process for making a tin plated metal article consisting of adjacently lying, intertwisted or interwoven metallic fine gauge constituent strands, said metal being capable of being tin plated and having a specific gravity of about 8.5, which comprises immersing said article in untinned condition in an alkaline stannate electroplating bath, electroplating tin upon each of said strands of said article to entirely cover each strand and until an amount of tin equal to 0.5 to 3% by weight of the article has been plated, thereby forming a tinned article in flexible condition each of whose constituent strands are plated with tin and separated from adjacently lying strands.

5. Process for making tin plated bunched or braided copper wire consisting of a plurality of fine gauge constituent strands regularly intertwisted or interwoven together, which comprises immersing untinned bunched or braided wire in an alkaline stannate electroplating bath, electroplating tin upon each of said strands of said wire to entirely cover each strand, and until an amount of tin equal to 0.5 to 3% by weight of the wire has been plated, thereby forming a tinned bunched or braided wire in flexible condition each of whose constituent strands are plated with tin and separated from adjacently lying strands.

6. Process for making tin plated bunched or braided copper wire consisting of a plurality of fine gauge constituent strands regularly intertwisted or interwoven together, which comprises immersing untinned bunched or braided wire in an alkaline stannate electroplating bath, electroplating tin upon each of said strands of said wire to entirely cover each strand and until an amount of tin equal to about 1 to about 2% by weight of the wire has been plated, thereby forming a tinned bunched or braided wire in flexible condition each of whose constituent strands are plated with tin and separated from adjacently lying strands, and removing the wire from the bath and rinsing and drying the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,159,510 Pavlish et al May 23, 1939 2,274,963 Hopper Mar. 3, 1942 FOREIGN PATENTS 14,591 Great Britain of 18-90 

1. PROCESS FOR MAKING TIN PLATED BUNCHED OR BRAIDED COPPER WIRE CONSISTING OF A PLURALITY OF FINE GAUGE CONSTITUENT STRANDS REGULARLY INTERWISTED OR INTERWOVEN TO GETHER, WHICH COMPRISES IMMERSING UNTINNED BUNCHED OR BRAIDED WIRE IN A POTASSIUM STANNATE ELECTROPLATING BATH, SAID BATH CONTAINING ABOUT 0.25 TO ABOUT 3.0 MOLS PER LITER OF POTASSIUM STANNATE AND ABOUT 0.15 TO ABOUT 3.5 MOLS PER LITER OF FREE POTASSIUM HYDROXIDE, OPERATING SAID BATH AT A CATHODE CURRENT DENSITY OF ABOUT 30 TO ABOUT 1000 AMPERES PER SQ. FT. AND A TEMPERATURE OF ABOUT 50* C. TO SUBSTANTIALLY THE BOILING POINT OF THE BATH, ELECTROPLATING TIN UPON EACH OF SAID STRANDS OF SAID WIRE TO ENTIRELY COVER EACH STRAND AND UNTIL AN AMOUNT OF TIN EQUAL TO ABOUT 1 TO ABOUT 2% BY WEIGHT OF THE WIRE HAS BEEN PLATED, THEREBY FORMING A TINNED BUNCHED OR GRAIDED WIRE IN FLEXIBLE CONDITION EACH OF WHOSE CONSTITUENT STRANDS ARE PLATED WITH TIN AND SEPARATED FROM ADJACENTLY LYING STRANDS, REMOVING THE WIRE FROM THE BATH AND RINSING AND DRYING THE SAME, AND HEATING THE PLATED WIRE UNDER NON-OXIDIZING CONDITIONS TO REFLOW THE TIN PLATE. 